Aluminum-zirconium compounds are well known as effective antiperspirants. The presence of zirconium species increases the efficacy of aluminum-zirconium antiperspirant by the depolymerization of aluminum species. This depolymerization is more important when activated aluminum antiperspirant solution is involved. However, zirconium species become further polymerized during the process.
U.S. Pat. No. 4,775,528 describes a solid aluminum-zirconium antiperspirant salt having HPLC peak height of peak 4 (or Band III) to that of peak 3 (or Band II) is at least 2. The method of making the antiperspirant of that patent involves mixing activated (HPLC peak 4 to peak 3 area ratio of at least 0:5) aluminum chlorohydrate solution with zirconyl hydroxy chloride solution at a temperature of at least 50° C. and quickly drying the solution.
U.S. Pat. No. 4,871,525 discloses aluminum-zirconium hydroxy halide glycinate complex having a peak height ratio of peak 4 to peak 3 of 0.5 to 1.8 and wherein peak (1+2) contains less than 4% of the polymer distribution by weight. The aluminum component is made by direct reaction of aluminum metal with AlCl3 or HCl at about 8–35% weight to weight concentration. The aluminum component, zirconyl hydroxy chloride and glycine of that solution are maintained at 50°–100° C. for a period of time. The solution is then dried.
Both U.S. Pat. No. 4,775,528 and U.S. Pat. No. 4,871,525 are silent regarding peak 5 (or Band IV) and apparently do not recognize the significance of maintaining control of the limits of the corresponding aluminum-zirconium antiperspirant. Also the processes of both patents polymerize the zirconium species to a greater extent because of the higher temperature treatment, which is believed to reduce the efficacy of the corresponding aluminum-zirconium antiperspirant salt.
European Patent 0 653 203 A1 teaches a process of making an antiperspirant active said to have an enhanced efficacy. The active is prepared by the reaction of activated aluminum component with zirconium complex. The zirconium sources are chosen to be the least polymerized so that depolymerized zirconium species are obtained in the final product. That reference, also, evidences no recognition of the distribution of aluminum species such as aluminum monomers and dimers or Band IV species, which is believed to be critical for the efficacy of aluminum-zirconium antiperspirant.
U.S. Pat. No. 6,375,937 describes aluminum-zirconium salts having metal to chloride molar ratio of about 0.9–1.2, and a glycine to zirconium molar ratio of greater than 1.3 while U.S. Pat. No. 6,436,381 relates to aluminum-zirconium antiperspirant salts with high peak 5 aluminum content of at least 33% wherein the antiperspirant salts have metal to chloride ratio of about 0.9–1.0.
Aluminum-zirconium antiperspirant with low M/Cl ratio such as those described in U.S. Pat. Nos. 6,375,937 and 6,436,381 tend to be more irritating to the skin than the corresponding salt with higher ratio. As a consequence, there is a tendency to add more amino acid in order to minimize the irritancy, and in turn this tends to reduce the efficacy of the aluminum-zirconium antiperspirant.
It is highly desirable to make an activated aluminum-zirconium salt, which is not an irritant to the skin and has enhanced efficacy. In accordance with the present invention it has been discovered that a novel activated aluminum-zirconium composition having a M/Cl ratio of about 1.20 to about 1.30 can be made in the presence of small amount of AlCl3 or HCl to have a maximum amount of depolymerized aluminum and zirconium species, and provides an antiperspirant that has enhanced efficacy and has a marked reduction in skin irritancy.
The activated aluminum-zirconium salts generally have characteristic HPLC Band III/II area ratio of at least 0.5, usually at least 1 with at least 80% aluminum is in Band III and II. There is no requirement on Band IV (or peak 5). In order to have the above HPLC profile, diluted aluminum-zirconium antiperspirant solutions are produced and dried. It is known in the art that that such diluted Al/Zr solution is very unstable. On aging the percentage of Band III decreases and the percentage of Band II increases. No study is known that reports on aging the changes in Band IV that consists of aluminum monomers and dimers. It has been only recently that higher a Band IV has been attributed to a higher efficacy of aluminum-zirconium antiperspirant, reference U.S. Pat. No. 6,436,381. On aging HPLC Band IV usually doesn't decrease. 27Al NMR, which reveals the structures of the aluminum species indicates that the amount of Al monomer decreases on aging as can be seen by references to Example 3 herein below. In accordance with the invention I have found that aluminum monomers and dimers generated in the activated aluminum-zirconium salt solutions are very sensitive to the reaction conditions. Different amount of aluminum monomers, dimers and polymers are produced under different reaction conditions and that is believed to affect the efficacy of the activated aluminum-zirconium salt. The changes in the structures of aluminum under different reaction conditions sometimes can only be observed using 27Al NMR, not by HPLC size exclusion chromatograph.